1. Field
Embodiments of the present invention relate to hot-plug technology and, in particular, to peripheral component interconnect (PCI/PCI-X) standard hot-plug controllers (SHPCs).
2. Discussion of Related Art
A peripheral component interconnect (PCI/PCI-X) bus is a bus in a computer system that interconnects a microprocessor and peripheral devices, such as keyboards, disk drives, video adapters, etc. A PCI/PCI-X bus has slots into which the adapter cards for the peripheral devices can be inserted or removed. Hot-plug technology allows a user to physically remove or insert one or more PCI adapter cards without having to remove power to the entire system or re-booting the system software. Only the individual PCI/PCI-X slots are affected and the other devices in the system are not disrupted.
Hot-plug controllers were being developed by various vendors that were compatible with the PCI Hot-Plug Specification, Revision 1.0, Oct. 6, 1997, PCI Special Interest Group, Portland, Oreg. It has been proposed that standardized hot-plug controllers be developed so that vendor-specific hot-plug controllers could be compatible across many platforms. The PCI Standard Hot-Plug Controller and Subsystem Specification, Revision 1.0, Jun. 20, 2001, PCI Special Interest Group, Portland, Oreg., (hereinafter “SHPC Specification”) was developed to meet this challenge.
The SHPC Specification provides that each slot for an adapter card have indicators, such as light emitting diodes (LEDs). For instance the SHPC Specification provides that there be two LEDs per slot, a power indicator (PLED) and an attention indicator (ALED). According to the SHPC Specification, each indicator is in one of three states: on, off, or blinking.
When the PLED is off, it is indicating that main power to the associated slot is off and that an adapter card may be safely inserted or removed from the slot. When the PLED is on, it is indicating that main power to the slot is on and that an adapter card may not be safely inserted or removed from the slot. When the PLED blinks, it is indicating that the slot is powering up or powering down and an adapter card cannot be safely inserted or removed from the slot.
When the ALED is on, it is indicating that an operational problem exists at the slot or adapter card. When the ALED is off, it is indicating that the slot and adapter card are operating normally. When the ALED is blinking, it is indicating that the system software is identifying the slot for a human operator to find. The SHPC Specification requires that when the PLED or ALED blinks, it blinks at a fifty percent duty cycle (±5%), such as 250 nanoseconds (ns) on and 250 ns off, at a prescribed frequency.
This indicator scheme has limitations, however, in that it does not communicate very much information about what the Standard Hot-Plug Controller (SHPC) is doing. The indicator scheme only shows whether a slot is active (the adapter card in the slot is powered), inactive (the adapter card in the slot is not powered), or in the process of changing states between being active and inactive, or vice versa.